VOR Navigation Basics for Aviators

Let's admit it. VOR navigation isn't the most user friendly way of getting around, but once you understand a few basics and some recipes on how to use the darned thing, it's really not that bad.

I am writing this blog post with the student pilot in mind, but hopefully the private pilot who never really understood VOR navigation will get something out of this posting.

There are two ways to work with VORs: the concept and the actual use. The concept is something you do with simulators at home or pencil and paper. A great and free simulator can be found here and I affectionately call it Tim's Airnav. Actual use as I describe below means understand what you want to do, then follow the recipe for that item. If you are in the cockpit and working on the conceptual part, you are in the wrong place. You should be home at the kitchen table. The cockpit is a great place to make sure you can use the VORs, but not a place to understand how they work.

There are three things you will normally do to navigate with VORs:

1. Intercept a radial and fly inbound (inbound means fly towards the VOR)
2. Intercept a radial and fly outbound (outbound means to fly away from the VOR)
3. Go direct from your current position to a VOR

Number 3 is really used once the radials mentioned in 1 and 2 are intercepted or it can be a "go direct to the blah-blah VORTEC directive from your instructor or air traffic control).

Now, before I go any further, some concepts we must agree on or we will not get anywhere.

A VOR station is a group of antennas on the ground that emit a radio signal. Your cockpit VOR receiver receives these signals and allows you to determine on which of 360 radials your aircraft is located. A radial is an electronic "line of position" (navigators say L O P). The radial are numbered 000 to 359. The 000 can also be referred to as the 360 degree radial. A technician turns a knob at the ground station and adjusts the radials so that the 000 (360) is pointing at magnetic north for that particular area. Remember that the angle of magnetic north from geographic north varies from point to point on the surface of the earth - that's why it's called "variance". Accounting for variation is important because you will follow this line with the combination of your magnetic compas and a needle on the omnibearing selector display called a course deviation indicator (CDI). A given VOR ground transmitter then reflects directions you see on your magnetic compass. More on this later.

Next concept, the radial. Think of the VOR transmitter as a dot on the ground from which 360 lines emanate. Each line is numbered 000-359. Each line is a radial. Whoops, I repeat myself, but I did it intentionally. A radial always comes FROM (note the emphasis on "from") the VOR. For example, the 090 radial (magnetic direction is always expressed in 3 digits with leading zero(es) if necessary) radiates from the VOR and makes a ground track towards magnetic east. It doesn't matter if I jump on the 090 degree radial and I fly towards the VOR or I fly away from the VOR, I am still on the 090 radial. Let's say that I fly towards the VOR on the 090. Inother words, I am flying magnetic west (towards 270). One mile away from the VOR I am still on the 090 and I am still flying west. A little later we are right on top of the VOR. At this point all the radials kind of come together - it's big mess and it's called the "Cone of Confusion". However, if I ignored the drunken CDI on my OBS display, it will eventually setting down as I keep heading west and if all were executed just right, I have crossed the VOR, left the 090 degree radial and now I am on the 270 degree radial heading away from the VOR and into the sunset.

I used a lot of words above to illustrate what I said earlier - all radials have a name and they have a start at the VOR - they emanate "FROM" the ground based VOR transmitter.

Now the part that messes up the beginner and a lot of experienced folks, the notion of the "TO" and the "FROM" flag on the omnibearing selector display. If you turn the dial (omnibearing selector) and you center the CDI and there is a "FROM" indication then the value you read at the top of protractor is the radial on which you are positioned. If you center the CDI and a "TO" indication is shown in the TO/FROM window, then you are on the radial indicated on the bottom of the protractor. Confused? If so, don't feel alone. It's not so bad once you understand the reason for this and it revolves around the fact that humans aren't good with flying using reverse sensing. To illustrate, suppose you want to fly on the 090 degree radial towards our VORTAC and cross the ground station and keep on going into the sunset on the 270 degree radial. Let forward into the future and say you have passed the VOR and you have 270 dialed into the your magnetic compas

Ok, now that we have established that let's talk about the 3 recipe items. Again, in order to execute one of the three recipes, you have to understand what you are trying to accomplish. For example, do you want to intercept a radial and go to the VOR station or do you want to intercept and fly away from the VOR station? With that in mind the recipes follows.